The present invention relates to a charge pump circuit, and more particularly to a charge pump circuit to be used for a high accurate analog control circuit.
FIG. 1 is a circuit diagram illustrative of a conventional charge pump circuit to be used for an analog control circuit. The conventional charge pump circuit comprises a CMOS circuit which further comprises a series connection of a p-channel MOS field effect transistor 701 and an n-channel MOS field effect transistor 702 between a high voltage line and a ground line. An output terminal is also connected to an intermediate point between the p-channel MOS field effect transistor 701 and the n-channel MOS field effect transistor 702. The p-channel MOS field effect transistor 701 is connected in series between the high voltage line and the intermediate point connected to the output terminal. A gate of the p-channel MOS field effect transistor 701 receives an UP-bar signal. The n-channel MOS field effect transistor 702 is connected in series between the ground line and the intermediate point connected to the output terminal. A gate of the n-channel MOS field effect transistor 702 receives a DOWN signal. Upon input of the UP-bar signal, the p-channel MOS field effect transistor 701 turns ON, whereby an output voltage is risen. Upon input of the DOWN signal, the n-channel MOS field effect transistor 702 turns ON, whereby the output voltage is fallen.
The p-channel MOS field effect transistor 701 and the n-channel MOS field effect transistor 702 have variations in dimension and impurity concentration and others due to manufacturing processes, for which reason the p-channel MOS field effect transistor 701 and the n-channel MOS field effect transistor 702 are different in drain current. Variation in the output voltage or the drain voltage causes variation in drain-source voltage such as a channel length modification, whereby the p-channel MOS field effect transistor 701 and the n-channel MOS field effect transistor 702 are different in drain current.
In Japanese laid-open patent publication No. 6-188728, a second conventional charge pump circuit is disclosed. FIG. 2 is a circuit diagram illustrative of the second conventional charge pump circuit to be used for an analog control circuit, wherein a series connection between a high voltage line and a ground line of a p-channel MOS field effect transistor 711 and an n-channel MOS field effect transistor 712 forms a charge pump. The second conventional charge pump circuit includes a current mirror 713 which controls a gate voltage of the n-channel MOS field effect transistor 712 so as to compensate variations between the p-channel MOS field effect transistor 711 and the n-channel MOS field effect transistor 712. Variation of the output voltage causes that the p-channel MOS field effect transistor 711 and the n-channel MOS field effect transistor 712 are different in drain current.
The conventional charge pump circuits have a problem with a difference between a voltage-rising width and a voltage-falling width even the pulse width remains the same. The reason for the problem is as follows. The p-channel MOS field effect transistor is used for the voltage-rising whilst the n-channel MOS field effect transistor is used for the voltage-falling. The p-channel MOS field effect transistor and the n-channel MOS field effect transistor are different in drain current due to the variations thereof on the manufacturing processes. Further, the p-channel MOS field effect transistor and the n-channel MOS field effect transistor have a difference in drain current de to source-drain voltage such as channel length modulation.
In the above circumstances, it had been required to develop a novel charge pump circuit which is capable of adjusting drain currents to be identical with each other between p-channel and n-channel MOS field effect transistors forming the charge pump circuit, whereby no substantive difference is caused between a voltage-rising width and a voltage-falling width, thereby realizing a highly accurate analog control circuit.